Please help the newbie

I just recently set up my two computers as a network, using an WRT54G. Computer A is hardwired to the router, and computer B is wireless. The main purpose of this network was to share a laser printer that is attached to B, and to allow file sharing.

It took me about a day, but I got the whole thing set up, and it was working just fine. That was about 3 weeks ago. Today the user on A went to copy a file into the shared folder on B, and got an error message. Don't have the exact message.

User on A is also not able to print to the laser. Trying to figure out what's wrong I went to My Network Places on both machines, and neither on is "seeing" the other one. (Both are XP Home SP2)

My question is this: If everything was set up and working then what could have changed so that neither computer can see the other anymore?

The firewall that I'm using is Zone Alarm, the free version. The level is set to High for the Internet Zone and to Off for the Trusted Zone. On each computer the other computer is in the list as a trusted host. The Windows XP Firewall is disabled.

I believe these settings are the same as they were when the sharing was working. Are there any other Zone Alarm settings that I should check?

Both computers are able to access the Internet, no problem. They just can't see each other through the router.

Well a few things come to mind. If you suspect its the firewall shut it off temporarily and if that part worries you then just unplug the wan side whilst you test. The other thing that comes to mind is how you were sharing the printers, if it was via file and print sharing, potential the netbios is having an issue. If you were sharing via the IP then potentially the machine with the printer attached has gotten a new dhcp address. If all else fails reboot everything, mayhaps one of the devices got a lil chocked up in one of its services.

I would like to thank all those who posted. I got things working again, but am not sure exactly what did the trick. I did reboot everything, and that was probably it. Sometimes the simplest things are the last things we try. It must be part of "human nature" to think a problem has to have some complicated solution.